Variable displacement engine have been used where one or more cylinder is deactivated (e.g., by closing intake and exhaust valves). In this way, increased fuel economy can be obtained during engine operating conditions that do not require full cylinder operation.
Vehicle system with variable displacement capabilities have also been described having hybrid powertrains. For example, US 2004/0035113 describes an approach where cylinder deactivation operation can be extended by providing additional torque from an electric motor. Further, activation/deactivation transitions are described using changes in throttle position with motor assist require before, during, and after the transition.
The inventors herein have recognized a disadvantage with such an approach. In particular, US 2004/0035113 generally requires consistent application of torque from the motor during cylinder deactivation conditions; however, this can continually drain the battery, especially during vehicle towing conditions or during long vehicle climbs. Furthermore, the inventors herein have also recognized that the transitions according to US 2004/0035113 may also result in degraded vehicle feel since a substantially constant motor torque is used, relying on rapid throttle changes to handle the torque disturbance. Specifically, even rapid throttle changes may be inadequate to provide acceptable vibration and drive feel during the transition.
In one example, at least some of the above disadvantages may be overcome by a vehicle system, comprising: a engine capable of disabling and enabling at least one cylinder; a motor coupled to said engine capable of absorbing torque and providing torque; and a controller for disabling and enabling said at least one cylinder, and during at least one of disabling and enabling, varying torque of said motor to compensate for transient changes in engine output torque caused by said one of disabling and enabling.
In this way, it may be possible to provide improved torque control during variation in the number of cylinders carrying out combustion. Further, such transitions may be performed with less energy loss due to spark retard. Further still, such transitions may be performed to increase stored energy. Finally, such transitions may be performed based on battery status to provide improved hybrid vehicle performance.
Note that there may be various approaches to disabling cylinders, including disabling intake and exhaust valves, disabling fuel injection (without disabling valves), or others.